Ladder boat for supporting wafers

Abstract

The present invention relates generally to an improved ladder boat for supporting semiconductor wafers during thermal treatments which comprises top and bottom plates vertically opposing each other and support rods secured to said plates. Said support rods are provided with dividers for supporting a plurality of wafers one above another in a parallel arrangement. The dividers have a special profile to include a ramp portion so that the wafer is seated at a sharp corner thereof. Therefore, the contact surface between the wafer backside at its periphery and the dividers is segmental or punctual. This contact is preferably performed outside the contact area between the wafer backside and the wafer support zones of the electrostatic chuck of the photolithography tool to be subsequently used in the course of the wafer manufacturing.

What is claimed is:  
     
       1. A ladder boat for supporting at least one semiconductor wafer for thermal treatment comprising: 
       (a) top and bottom plates vertically opposing each other and parallel in a horizontal direction;  
       (b) a plurality of support rods secured to said top and bottom plates to define an internal volume therebetween and which are provided with at least one divider to support said wafer,  
       wherein said wafer divider is profiled to have a ramp portion so that said wafer is seated on a sharp corner thereof, the contact surface being limited to a segment of line disposed on a circle that is concentric to said wafer periphery and is spaced therefrom to avoid microscratches and chipping particles during said thermal treatments. 
     
     
       2. The ladder boat of  claim 1 , wherein contact surface between said wafer backside at its periphery and said divider is segmental or punctual. 
     
     
       3. The ladder boat of  claim 1 , wherein angle of said ramp in the horizontal direction is greater than about 2°. 
     
     
       4. A ladder boat for supporting at least one semiconductor wafer for thermal treatment comprising: 
       (a) top and bottom plates vertically opposing each other and parallel in a horizontal direction;  
       (b) a plurality of support rods secured to said top and bottom plates to define an internal volume therebetween and which are provided with at least one divider to support said wafer,  
       wherein said wafer divider is profiled to have a ramp portion so that said wafer is seated on a sharp corner thereof, wherein said angle of said ramp in the horizontal direction is about 3°. 
     
     
       5. The ladder boat of  claim 1 , wherein at least three support rods support said wafer so that said wafer is supported at only three points. 
     
     
       6. The ladder boat of  claim 1 , wherein at least three support rods support said wafer so that said wafer is supported at only three points, and wherein said points are separated by an angle of 90°. 
     
     
       7. The ladder boat of  claim 1 , wherein cross-sectional area for said support rods is selected from a group consisting of a circular area, rectangular area, square area, elliptical area and triangular area. 
     
     
       8. The ladder boat of  claim 1 , wherein cross-sectional area for said divider is selected from a group consisting of a circular area, rectangular area, square area, elliptical area and triangular area. 
     
     
       9. The ladder boat of  claim 1 , wherein cross-sectional area of said wafer divider is minimum at the contact junction with said support rod. 
     
     
       10. The ladder boat of  claim 1 , further comprising at least two additional rods which are not provided with dividers to improve rigidity thereof. 
     
     
       11. The ladder boat of  claim 1 , further comprising at least two additional rods which are not provided with dividers to improve rigidity thereof, and wherein each additional rod being placed between two support rods. 
     
     
       12. A ladder boat for supporting at least one semiconductor wafer for thermal treatment comprising: 
       (a) top and bottom plates vertically opposing each other and parallel in a horizontal direction;  
       (b) a plurality of support rods secured to said top and bottom plates to define an internal volume therebetween and which are provided with at least one divider to support said wafer,  
       wherein said wafer divider is profiled to have a ramp portion so that said wafer is seated on a sharp corner thereof, and wherein contact surface between said wafer backside at its periphery and said divider is segmental or punctual, and wherein said segmental or punctual contact is performed outside the contact area between the wafer backside and the wafer support zones of an electrostatic chuck of a photolithography tool to be subsequently used in the course of wafer manufacturing.